Donor Lymphocytes Collection: Lymphocytes are a type of white blood cell involved with the immune system. Your original marrow/stem cell donor will undergo one white blood cell collection procedures called leukapheresis. Blood from the vein in one arm will be circulated through a special machine to remove the white blood cells, and the rest of the blood will be returned to the donor's other arm. The cells collected from the leukapheresis will be sent to the laboratory where the amount of white blood cells collected will be measured. A sample will be removed for study testing, and the remaining lymphocytes will be set-aside for infusion.